When raw fruit and vegetables are subjected to mechanical injury, e.g., peeling, cutting, slicing, crushing, etc., enzymatic browning usually occurs. This enzymatic browning results from the polyphenol oxidase--catalyzed oxidation of phenolic compounds to O-quinones, which polymerize to form dark-colored pigments. This discoloration of fruit and vegetable products presents a serious problem in the food industry. Such products deteriorate in both taste and appearance and are thus not appealing to consumers. Consequently, a significant amount of fruit and vegetable product must be either drastically reduced in price or discarded. This results in a substantial financial loss to the food industry.
Sulfites were used in the food industry for some time to inhibit enzymatic browning in cut fruit and vegetables, as well as in juices. However, it was discovered that sulfites are a significant health threat to people with certain ailments, such as asthma. Consequently, the use of sulfites in fresh food products such as fruits and vegetables, and their juices, was banned. Because of this ban, much effort is being expended to find acceptable and economical substitutes for sulfites. Currently, the alternatives to sulfites for use in fresh cut fruit and vegetables include additive blends of ascorbic or erythorbic acid, food-grade phosphates, citric acid, dextrose, sodium or calcium chloride, or cysteine and potassium sorbate. See "Sulfite Alternative Blend Extends Fruit, Vegetable
Freshness"; Duxbury, Dean D., Food Processing, Nov. 1986, pp. 64 & 66. While such alternatives show promise, they do not penetrate plant tissue as readily as sulfites do and can be oxidized over time. Thus, their effects are less than, or do not last as long as, that of sulfites.
It has also been reported that ascorbic acid derivatives such as ascorbic acid - 2 -phosphate and ascorbyl-6-palmitate, can be used either alone, or in combination with an acidic polyphosphate, to inhibit the browning of mechanically injured raw fruit and vegetable products. See U.S. Pat. No. 4,814,192. Further, it is taught in U.S. Pat. No. 4,975,293 that soluble cyclodextrins, either alone or in combination with an acidic polyphosphate, can also be used to inhibit browning. While these alternatives show promise, the acidic polyphosphate and cyclodextrin are not yet approved for food use.
U.S. Pat. No. 4,959,230 teaches the use of an edible thixotropic gum, which may be a carrageenan, and an edible organic acid for inhibiting deterioration and extending the shelf life of fresh fruits and vegetables. There is no suggestion of the treatment of juices. The fact that specific chemical agents can be used for inhibiting deterioration of freshly cut fruit and vegetables does not necessarily mean that the same agents can be used to inhibit deterioration of juice from the same fruit and vegetables. For example, ascorbic acid-2-phosphate and -triphosphate showed promise for inhibiting browning of cut surfaces of various fruit and vegetables, but were ineffective for juice. Also, while cinnamate and benzoate inhibited browning in juice, they induced browning when applied to cut surfaces. Further, combinations of .beta.-cyclodextrin with ascorbic acid, ascorbic acid-2-phosphate, or ascorbyl palmitate, were effective in juice but not on cut surfaces. Combinations of ascorbic acid with an acidic polyphosphate were highly effective with both juice and cut surfaces. See, "Control of Enzymatic Browning in Apple with Ascorbic Acid Derivatives, Polyphenol Oxidase Inhibitors and Complexing Agents"; by G. M. Sapers et al.; Journal of Food Science: 1989; pp. 997-1002 & 1012. Thus it can be appreciated that one cannot predict with any certainty an agent's anti-browning properties for juice, given its effect on freshly cut fruits and vegetables, and vice versa.
While various chemical agents have been developed as sulfite substitutes for the inhibition of browning of cut fruit and vegetables, as well as for juices, there still remains a need in the art for more effective substitutes for sulfites. This is especially true for those agents which have already been approved for food use, not only on fresh fruit and vegetables, but also for use in juices.